Field of the Invention
The present invention relates to an image forming apparatus adopting an electrophotography method such as a copying machine, printer, facsimile apparatus, or plate making system.
Description of the Related Art
In an image forming apparatus, toner images of respective colors (for example, cyan, magenta, yellow, and black) are formed using laser beams, and the toner images of these colors are superposed with each other, thus forming an image. In this case, when the toner images of the respective colors have different sizes, color misregistration occurs. To avoid such problem, Japanese Patent Laid-Open No. 2000-238342 discloses an arrangement in which a slight delay is inserted or deleted into or from an image data stream, thereby adjusting a laser write frequency.
However, in the arrangement described in Japanese Patent Laid-Open No. 2000-238342, tolerances of respective reflection surfaces of a rotating polygon mirror are not corrected, thus causing length variations of scanning lines formed by the respective reflection surfaces. As a result, moiré that brings visual discomfort may be generated due to an interference between cycles of the rotating polygon mirror and a screen. For this reason, a limitation which inhibits use of a screen that readily causes moiré with respect to the cycle of the rotating polygon mirror has to be set.